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Colder climate and oxygen-rich ocean currents laid the foundations for modern marine ecosystems

Quarry. Photo.
The Hällekis quarry in Västergötland hosts Middle Ordovician limestone layers that have been sampled and analysed in the study. Photo: Anders Lindskog.

Changes in oxygenation and climate had a fundamental impact on marine environments and ecosystems during one of the most transformative times of the development of life on Earth. This according to a new study in which researchers have analysed iodine and calcium in limestone samples from Sweden, Estonia and Russia.

There has long been speculation about major links between biodiversity and access to oxygen in the early stages of animal evolution, but it is difficult to estimate the amount of oxygen that far back in time. In a new study published in the scientific journal Nature Geoscience, a team of researchers led from Lund have succeeded in unravelling part of the puzzle around potential links.

The researchers have studied oxygen levels in the shelf sea that covered our continent (Baltica) during the Ordovician period. Through advanced analyses of the elements iodine and calcium in a large collection of limestone samples from Sweden, Estonia and western Russia, they have been able to map out and visualise how oxygen levels varied over time and space during a period of around 20 million years (~477–457 million years ago).

“The results show remarkable co-variation between oxygenation, climate and environmental changes as well as marine biodiversity. A colder climate and ocean currents helped oxygenation, which, in turn, benefitted animal life. These changes effectively laid the foundations for modern marine ecosystems and habitats,” says Anders Lindskog, geology researcher at Lund University.

For the Ordovician period, theoretical models have previously suggested that biodiversity benefitted from increased oxygen levels, but empirical data have been lacking. The new study contributes comprehensive and unique information about marine oxygenation and its impact on contemporary fauna. The study is particularly interesting since the observed links between climate, environment and organisms in the distant past, without anthropogenic influence, give us important information about what we can expect in the future.

“There is worry that the current warming of the climate will have a long-term negative impact on living conditions in marine environments, including through decreased oxygen levels. Our results suggest that these worry are well founded,” says Anders Lindskog.

The study provides an important piece of the puzzle about the history and development of life itself. By understanding how life “behaves” in relation to climate and environment across time and space, researchers gain further reference frameworks for more reliable forecasts.

“We went into this study with a notion that there might be a certain co-variation between oxygen levels and biodiversity, but we were surprised that the relationship was so strikingly clear,” says Anders Lindskog.

Alongside Lund University, Florida State University participated in the project.

The study “Oxygenation of the Baltoscandian shelf linked to Ordovician biodiversification” is published in the research journal Nature Geoscience.

Read the study (

Text: Johan Joelsson.